MB_CoilRd()

MB_CoilRd() is called when a Modbus master sends a Function Code 1 command. MB_CoilRd() returns the value of a single coil. MB_CoilRd() should only be called by µC/Modbus.

Prototype

CPU_BOOLEAN MB_CoilRd (CPU_INT16U coil,
CPU_INT16U *perr)

Arguments

coil

Is the coil number that you want to read and can be a number between 0 and 65535 (depending on your product). It is up to you to decide which coil is assigned to what variable in your product.

perr

Is a pointer to a variable that will contain an error code based on the outcome of the call. Your code thus needs to return one of the following error codes:

MODBUS_ERR_NONE

if the coil number you specified is a valid coil and you are able to have code access the value of this coil.

MODBUS_ERR_RANGE

if the coil number passed as an argument is not a valid coil number for your product.

Returned Value

MB_CoilRd() returns the current value of the specified coil number (TRUE or FALSE). If an invalid coil number is specified, you should return FALSE.

Notes / Warnings

Code is enabled when MODBUS_CFG_FC01_EN is set to DEF_ENABLED in your product’s mb_cfg.h file.

Called By:

MBS_FC01_CoilRd() in mbs_core.c

Example

In this example, our product has 163 coils. 160 coils are placed in a table called AppCoilTbl[]. The other three coils are actually variables that we treat as coils to allow a Modbus master to read the status of those values. The first 160 coils are assigned coil numbers 0 to 159. Coil numbers 200, 201 and 202 correspond to the following application variables: AppStatus, AppRunning and AppLED, respectively.

CPU_INT08U   AppCoilTbl[20];
CPU_BOOLEAN  AppStatus;
CPU_BOOLEAN  AppRunning;
CPU_BOOLEAN  AppLED;
 
CPU_BOOLEAN  MB_CoilRd (CPU_INT16U coil, CPU_INT16U *perr)
{
    CPU_INT08U  ix;
    CPU_INT08U  bit_nbr;
 
 
    *perr = MODBUS_ERR_NONE;
    if (coil < 20 * sizeof(CPU_INT08U)) {
        ix      = coil / 8;
        bit_nbr = coil % 8;
        if (AppCoilTbl[ix] & (1 << bit_nbr)) {
            return (TRUE);
        } else {
            return (FALSE);
        }
        return (val);
    } else {
        switch (coil) {
            case 200:
                 return (AppStatus);
    
            case 201:
                 return (AppRunning);
 
            case 202:
                 return (AppLED);
 
            default:
                 *perr = MODBUS_ERR_RANGE;
                 return (0);
        }
    }
}